Coupling between balanced and unbalanced circuits



May 16, 1950 A. E. HARRISON COUPLING BETWEEN BALANCED AND UNBALANCED CIRCUITS Filed April 2, 1948 UNBALANCED" 2 Shee ts-Sheet 1 ax/M ATTORNE Y May 16, 1950 A. E. HARRISON COUPLING BETWEEN BALANCED AND UNBALANCED CIRCUITS 2 Sheets-Sheet 2 Filed April 2, 1948 I INVENTOR. ARTHUR E. HARRISON a mi ATTORNEY of both circuits as well as between the conductors .of the balanced circuit and. ground, thus permit- =currents, and introducing ,,vo1tage loops whereby furtherinsulation problems are created. Various i arrangements h ve en r e r i QREiFtfiQiQiiifiF? ti ii tl-n i W1 iore tf rse i nat neprm n mizi sn hes vs ra it m e fir q n fi 1 h,1s adcape es s id .a ran ements, howe r in: volying in most instances complicated or bulky uctu es-i U aniiu y ee e ij t ts. r. m y ca a i nce? re l g l ei mine e pling balanced and unbalancedcii'fcuits, I vice being" adapted to minimize the new; of stray :currents and to prevent the formation of iin'de sirable voltage l'o'op's'.

ta' couplin'g ar angement or w bulltjt'o be used L n o. particularly in mobile hi nfrequeney transmit: v w or the 'ff qu 's mplbyed. T e jim- Patented May 16, 1950 I r UNITED STATES ATENT 2,507,7i2 oo'tiPiiritGjihrrWEEN enmelib 5&1;

' YUNBAL'ANCED CIRCUITS Arthur- E. Harrison, Short inns,'i.,*z sis if nai to Bell vTelephoneLabpratories, lnc'iirporated, New York, N. Y., a corporation of New York iip iieatiem rii '2, 1948 S eri ai M18312; i 11 meet. (01. 178-44) 1 This invention relates to electric wave transmission systems and, more particularly, to coupling'devices for high frequency signaling systems.

In high frequency systems, difficulties are often 5 s,

encountered in designing coupling devices for a coupling balanced and, unbalanced circuits. between thel These difficulties are for the most part caused by 9i this hecher tv'i stray capacitances which have a tendency to c p ugtgr p disturb the relationship between the conductors unb 1a edload ting the flow .01 nundesirednandv unpredictable A-nc pject o'rih iti t f iifi l S n 9 .1 9 2 balanced in which theeffects of A further object or the invest-6m t6 pr" tie ears or receivers. V V v M neod n e p, nduqt zeprp yhwstiil'another'objectoi theini entibil. is to pro: ivf' t ,ej i d ne on 'vide means f or'at least'partly'resonati g th iefthx 1.031 bf 136M112? I ductance of a loop fo'rmingthecbuplin The fcapacita ngfbetweeii th"e, cfori :a balanced and a unbalancedcircuifis id'm ductor e ements; (1,11 er the device satin; also'serving to diminish the flow of parasitic curcir iiitjor highfffrequenc'y currents through the coupling and thetwo "circuits. d in the mqe m by the currents'fiewf The manner in which these 'andiotherobjects" tors sand '4' of the balanced line 5 and features of the invention are attain'eglj will be At the "sametime", this capacitance will "at least described connection with the following deonate the inductance of 'theloop l'fl, i e desqription Of e i v n bn ak nl n n-' efl s l thejim ed nc reb ndim junction with the accompanying drawing in are mg theehiciency of the'eoupling arrangeis a schematic circuitdiagramshowing a It will be understood'that, at the frequencies coupling arrangement according to the inven co'nt'emplal 'straycurrentswm also tend to tion; butedeapaeitancesexistine Figs 2 :3 and 4 are similar diagramsshowiiig I and, 'l 1 on one hand and modifications of the coupling arrangement i1- I Sja'hd'll on the other. "Qiiig lustrated in Fig. 1;and I v Y J from eoeduetor' 4 to Fig; 5 is a detailed View 'of a coupling dew? .o o. point 2! where-me accordingto the invention as used in the circuit v, M corin ctedf to conductor it, part of the arrangements of the preceding figures. 88 current flowing" through conductor I4 and part through conductor I6, the latter current returning to the source I by way of the aforesaid capacitance between conductors II and 3. The current passing through conductor is will again divide at point 20, part going through the load and returning by way of conductors 9, l and II, the other part flowing to ground through the impedance [9.

That part of the stray current which, branching off at or near point 2|, flows through conductors i6 and II must first pass along the inside of the tubular sheath l'l before reaching inner conductor element I6 across the interelement capacitance of the device [2. Thus it will be seen that the path of this current is substantially longer than it would be if device l2 were replaced by a single conductor and that, furthermore, the said interelement capacitance introduces an additional impedance into this path whereby the magnitude of this undesirable current will be decreased. At the same time it can be shown that this capacitance also tends to improve the phase angle of the stray current, with respect to the induced current, in such a manner that the former will no longer oppose, but will, at least to a certain extent, reinforce the latter whereby the efficiency of the coupling arrangement will be further enhanced.

The arrangement shown in Fig. 2 diifers from that just described in that, in this case, the sheath ll of the device 12 is connected to transverse loop conductor 13 while the inner conductor element it is connected to grounded conductor M. It will be seen that the interelement capacitance of device i2 is here inserted in the path of that part of the stray current which flows toward point 26. Most of the stray current power passing through conductor l3 will, however again have to pass along the inner surface of sheath ll, thus following a path of increased length.

The modification shown in Fig. 3 is similar to that illustrated in Fig. 1, except that conductor l4 now connects the point 2| on sheath ll with the center conductor 9 of the unbalanced load "I, the outer grounded load conductor 8 being here connected to conductor [5 of the loop l0. With this arrangement, the stray path to ground for energy from balanced line 5 leads over the capacitance between conductors 3 and H which, normally, will be less than the capacitance between conductor 4 and sheath ll so that the magnitude of this parasitic current will be reduced.

The modification shown in Fig. 4 combines some of the features of the modifications shown in Figs. 2 and 3 in that the sheath [1 is connected by way of loop conductors [3, H and IE to the cable sheath 8, inner conductor I6 being now connected to the central cable conductor 9 by way of loop conductor M. The functioning of this arrangement will be clear from the foregoing description.

As shown in Fig. 5, the tubular conductor ll of the device l2 preferably consists of a metallic shell conductively surrounded by a metallic ring 22, the latter being joined to a portion 23 of a conductor which may be the element 14 or l3 in Fig. l or 2, respectively. Inner conductor I6 is held in spaced relation relative to shell I! by means of a tubular body 24 of insulating material which, as shown, projects beyond the end of conductor l6 at the right and beyond the end of conductor H at the left. The conductive member I6 is integral with a conductor portion 25 which may represent part of element l3 or II in Fig. l or 2, respectively.

Although the invention has been described and illustrated with reference to certain specific embodiments, it is to be understood that various modifications and adaptations thereof will be within reach of those skilled in the art and may be resorted to without departing from the spirit or exceeding the scope of the invention as defined in the objects and in the appended claims.

What is claimed is:

1. A device for coupling a pair of balanced and a pair of unbalanced conductors, comprising a conductive loop having two galvanically separated branches, a metallic sheath conductively connected to one of said branches, said sheath insulatedly surrounding a portion of the other branch of said loop, another portion of said loop extending adjacent one of said balanced conductors in spaced relation thereto, said sheath extending adjacent the other of said balanced conductors in spaced relation thereto, and means connecting each of said branches to a respective one of said unbalanced conductors.

2. A device according to claim 1 wherein said sheath is grounded.

3. A device according to claim 1 wherein the portion of the loop surrounded by said sheath is grounded.

4. A coupling between an unbalanced and a balanced circuit, comprising a conductive loop having two substantially parallel portions and a transverse portion connected across respective ends thereof, one of said parallel portions comprising a linear element and a tubular element insulatedly surrounding said linear element in spaced coaxial relation thereto, one of said elements being conductively connected to said transverse portion, means conductively connecting the end of the other of said elements remote from said transverse portion to a conductor of said unbalanced circuit, and means conductively connecting the end of the other of said parallel portions remote from said transverse portion to another conductor of said unbalanced circuit.

5. A coupling according to claim 4 wherein said remote end of the other of said elements is grounded.

6. An electrical transmission system comprising an unbalanced and a balanced circuit, a source of high frequency energy connected in one of said circuits, a load connected in the other of said circuits, and means electromagnetically coupling said two circuits, said means including a loop having two substantially parallel portions and a transverse portion connected across respective ends thereof, one of said parallel portions comprising a linear element and a tubular element insulatedly surrounding said linear element in spaced coaxial relation thereto, one of said elements being conductively connected to said transverse portion, means conductively connecting the end of the other of said elements remote from said transverse portion to a conductor of said unbalanced circuit, and means conductively connecting the end of the other of said parallel portions remote from said transverse portion to another conductor of said unbalanced circuit.

'7. A system according to claim 6 wherein the physical extent of each of said portions is small relative to the wavelength of said high frequency source.

8. A system according to claim 6 wherein said high frequency source is connected in the balanced circuit.

9. In a high frequency electric wave transmission system having a driving circuit including a Lecher wire transmission line having two conductors and a driven circuit comprising a first coaxial transmission line having an inner conductor and an outer conductor coaxial with said inner conductor, one of said circuits being balanced and the other unbalanced, coupling means for coupling said circuits, said coupling means comprising a single turn coupling loop including a second coaxial line, one portion of said coupling loop being adjacent to one of said Lecher wire conductors and another portion of said coupling loop including said second coaxial line being adjacent to the other of said Lecher wire conductors, said second coaxial line having an inner conductor conductively connected by a portion of said coupling loop to one of the conductors of said first coaxial line, said second coaxial line also having an outer conductor coaxial with the inner conductor of said second coaxial line and conductively connected by another portion of said coupling loop to the other conductor of said first coaxial line, and said second coaxial line also having insulating means for electrically insulating its inner conductor from its outer conductor.

10. A high frequency electric wave transmission'system in accordance with claim 9, wherein the inner conductor of the second coaxial line is conductively connected by a portion of the coupling loop to the inner conductor of the first coaxial line and wherein the outer conductor of the second coaxial line is conductively connected by another portion of said coupling loop to the outer conductor of the first coaxial line.

11. A high frequency electric wave transmission system in accordance with claim 9 wherein the inner conductor of the second coaxial line is conductively connected by a portion of the coupling loop to the outer conductor of the first coaxial line and wherein the outer conductor of the second coaxial line is conductively connected by another portion of said coupling loop to the inner conductor of the first coaxial line;

ARTHUR E. HARRISON.

REFERENCES CITED UNITED STATES PATENT Name Date Swart Feb. 10, 1942 Number 

